1. Field of the Invention
This disclosure relates to a system for obtaining and scanning an impression of the plantar surface of the foot. This disclosure further relates to a system for obtaining and scanning a contour of an impression of the plantar surface of the foot that uses a self-contained laser scanning technology to digitize the contour of the impression for orthotics manufacture. This disclosure further relates to a system for obtaining and scanning an impression of the plantar surface of the foot that uses a calibration plate that reduces aberration and distortion of the scanned image.
2. Description of Related Art
Traditionally, devices for the purpose of capturing the three dimensional (3-D) shape or contour of the plantar surface of the foot require a foam impression that is filled with plaster. The resulting plaster is used to produce a model of the subject foot of the patient. The model can then be measured using a pin digitizer or a laser scanner to accurately create a representation of the plantar surface of the foot for orthotics manufacture. Systems that use plaster are inconvenient, require numerous steps and are time consuming. The laser scanning systems, while not requiring plaster, are not generally self contained or efficient.
Systems using optical digitization of a three dimensional (3-D) contour using a camera coupled with a light source for triangulation are known. Typically, the light source is structured or beamed; a beamed source would include a laser line projected at a proscribed incident angle onto an object within the camera field of view. Optical digitization systems are typically calibrated to map observed line location to contour data. Placing a predefined geometrical object in the camera field of view and mapping each point in the image to the known location on the object can realize the calibration. The recorded image data is compared with the known geometry of the object in the field of view to determine and assign geometry values to the observed location in the camera's image data. In this fashion, the system learns how to derive geometric data from point locations in the camera image. That is, the digitization system is calibrated.
There are a number of variations of the above-discussed concept. For example, one variation uses a calibration plate disposed between the light source and the surface to be scanned. The light passing through the calibration plate forms a pattern, such as a matrix of lines, a grid pattern, dots, etc. on the surface to be scanned. Alternatively, the digitization system may use a polar axis rather than a linear axis for the transport of the object being measured through the field of view of the camera and the structured light source. Such systems often have problems related to aberration and distortion of the image that is viewed by the camera, as well as inconsistency in brightness due to distance and angle of reflection.
Systems using the basic optical digitization discussed above are known. However, heretofore such systems have been large, expensive to build time and consuming to operate. This and other disadvantages limit the application of the laser scanning technology to applications where expense and size are not relatively important factors such as applications like high-end medical applications and service bureaus.
Other technologies may be used to measure the geometry of the undersurface of the object to be measured, such as a foot. These technologies include (1) contact digitizing wherein gauge pins spaced at known intervals are urged upward beneath the foot and sample the contour periodically, and (2) optical triangulation where radiation of a known characteristic is projected against the subject foot such that the resulting shape of the radiation as it contacts the foot is observed by a sensor, typically a camera. A processor is used to evaluate the observed image to determine the contour data of the object (e.g., the foot) being measured.
Contact digitizing is generally the preferred method of obtaining the underside of a foot when the merits of the resulting data are the exclusive criterion. A contact digitizer supports the foot while measuring. Supporting the foot allows a full weight bearing measurement to be made, while not allowing the foot to completely collapse against the flat, top surface of the scanner. This yields a supportive data set that captures the extension of the foot when weight is applied.
A laser scanner has a clear plate between the scanning mechanism and the subject being measured. In the instance of measuring a foot, if the foot is suspended above the glass plate the data produced by the scanner matches the shape of the foot. However, this technique requires that the foot be measured in an unweighted position. The contour data obtained from the foot in the unweighted position is not very desirable since the foot can expand by as much as size and one-half when weight is applied thereto in the course of walking. The contour produced by an unweighted measurement will over-support the foot and cause discomfort. Yet, if the foot is placed against the clear plate to simulate the weight bearing of the foot, the bottom of the subject foot is completely flat. This produces an uncomfortable and unnatural, distorted shape.
Laser scanners also have a number of other problems associated with placing the foot against the clear plate such as (1) fogging where, if the foot is not completely dry, a fog is produced on the glass that tends to compromise the measurement accuracy of the foot since the shape of the subject foot is at least partially obscured by the fog; and (2) surface refraction caused by a lack of contrast of the subject foot due to, for example a light skin tone of a bare foot placed against the clear glass plate that disperses the projected radiation when it contacts the foot. The projected light disperses inside the body. It then refracts back through the clear plate. This produces an ambiguous radiation observation, as the radiation is diffused.
Accordingly, there is a need for a system that obtains a impression of the plantar surface of the foot coupled with the advantages of a laser scanning systems, as discussed above. Such a system would be of similar efficacy in acquiring data from any kind of medium used to capture a foot impression.
Alternative mediums to the use of foam for obtaining an impression of the foot, and particularly the plantar surface of the foot, also exist. One such common alternative medium is a sock casting, often called a “slipper cast”. This technique involves encasing the foot in a casting material that hardens when activated. Once hardened, the casting is cut and removed from the foot. Removing the top portion of the casting then produces an impression of the foot. At that point it can be processed identically to a foam impression using a scanner.